Conventional hybrid engine systems generally include both an electric motor and an internal combustion engine that are capable of powering the drivetrain in order to propel the car. A hybrid vehicle can have various configurations. For example, in a parallel configuration both the electric motor and the internal combustion engine are operably connected to the drivetrain/transmission to propel the vehicle. In a series configuration, the electric motor is operably connected to the drivetrain/transmission and the internal combustion engine indirectly powers the drivetrain/transmission by powering the electric motor.
In these configurations, the electric motor, which may also function as a generator, is connected to the input shaft of the transmission (i.e., engine side of the transmission) as opposed to the output shaft of the transmission (i.e., the wheel side or power delivery side of the transmission). Thus, during regenerative braking, the gears in the transmission directly affect the rotation speed of the electric motor/generator because the electric motor/generator is operably connected to the input shaft of the transmission. In other words, the electric motor/generator is on the opposite side of the transmission from the wheels and thus the transmission governs the rotation speed of the electric motor/generator during regenerative braking.
In conventional vehicle systems, a transmission control unit controls the gear shifting and general operation of the transmission. Conventional transmission control units are configured and tuned to automatically shift gears without considering the effect that a gear shift may have on the ability of the electric motor/generator to produce electricity. Thus, downshifting and/or other shifting events during a regenerative braking procedure may cause the electric motor/generator to rotate at speeds that are outside optimal efficiency ranges or outside specific operability ranges. In such situations, not only is the efficiency of the power regeneration technique diminished, the electric motor/generator may be damaged as it operates outside generally recommended speed ranges. Further, conventional transmission controllers may cause the transmission to repeatedly, although temporarily, disengage the generator from the wheels, thus repeatedly sacrificing time that could otherwise be spent generating electricity.